1. Field of the Invention
The present invention relates to a linear motion transmission apparatus and its chain.
2. Description of the Prior Art
Referring to FIGS. 1 and 1A, a conventional chain structure for a motion transmission apparatus comprises includes a plurality of spacers 511 and two links 512 at both sides of the respective spacers 511 for connecting them together so that a plurality of rolling elements 513 roll within the spaces defined by the spacers 511 and the links 512. If this conventional chain structure is an assembly structure, it will cost a lot of time and manpower to assemble spacers 511 and the links 512 together into a chain structure. If the spacers 511 are unitary with the links 512, the spacers 511 are concave structures from the point of view of mold design, which will lead to the occurrence of undercut during demolding. Using rolling elements as a mold core to produce the chain has the disadvantages of low production efficiency and that the oil on the outer surface of the rolling elements can easily be scrapped off.
Referring to FIG. 2, another conventional chain structure 61 for holding the rolling element 513 comprises a plurality of spacers 611 and two links 612 connected at both sides of the spacers 611. The disadvantage of this conventional chain structure is that, during injection molding, a thin and long cylindrical member must be used as a core in order to form the circular aperture 613 in the respective spacers 611, and after forming of the product, it has to use a complicated transmission mechanism to push or pull out the cylindrical member. However, the formed product will tightly embrace the cylindrical member after cooling off, making it difficult to pull out the cylindrical member. Meanwhile, the pulling action might cause burrs on the formed product. Furthermore, the rolling element 513 is in linear contact with the inner diameter of the circular aperture 613, the contact area is a closed space, and the linear contact has a relatively large contact pressure which makes it difficult for the oil film to pass through the contact surface, and as a result, the lubricant oil is more likely to be scraped off.
When the rolling element 513 rolls along the rolling path (not shown), the contact area of the rolling element 513 with respect to the rolling path is defined as a load area which is approximately annular (as indicated by the slanting lines on the outer surface of the rolling element in FIGS. 1 and 2). Since the load area 111 keeps contacting the rolling path, the lubricating oil thereof will continuously be pushed to the areas at both sides of the load area 111, as a result, the areas at both sides of the load area 111 are covered with lubricating oil, but the annular load area 111 that needs to be lubricated is not sufficiently lubricated.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.